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Hadrosaurid ornithopods from the early to middle Campanian are rare in North America, but the Wahweap Formation of southern Utah yields specimens that are increasing the known diversity of hadrosaurids from this poorly understood time period. A new genus and species of lambeosaurine hadrosaurid, Adelolophus hutchisoni, is described on the basis of an isolated maxilla. This single element is distinct from all other known lambeosaurine hadrosaurid maxillae in the large medial wall, raised palatine process, and other features associated with the raised medial wall. Another locality in the middle of the Wahweap Formation yielded two individuals of presumably the same species, an adult and a juvenile. The specimens show autapomorphic morphology of the caudal vertebrae neural spines and centra, along with a unique suite of iguanodontian characters. Given that the only diagnostic skull elements belong to the juvenile individual, the phylogenetic position of this species is unclear, although the postcranial skeleton possesses a mix of primitive and derived traits. The site represents a swampy environment containing autochthonous specimens; among these, long bones exhibit slightly preferred orientations.

Introduction

In contrast to the long history of Cretaceous dinosaur collecting in Montana, United States, and Alberta, Canada (Currie, 2005), southern Utah, United States, has been intensively prospected for dinosaurs only since 2000. As in other North American terrestrial formations, hadrosaurid dinosaurs are some of the most common fossils discovered in southern Utah, and are providing important data on biogeographic patterns and paleoecology of Campanian dinosaurs (Gates and Evans, 2005; Gates et al., 2010). The hadrosaurids from the Kaiparowits Formation (late Campanian) are becoming well known, with multiple specimens of the two known species of the saurolophine Gryposaurus, G. notabilis? (Gates et al., 2013) and G. monumentensis (Gates and Sampson, 2007). The only lambeosaurine known from the formation is an undetermined species of Parasaurolophus (Gates et al., 2013). The Wahweap Formation underlies the Kaiparowits Formation within the Grand Staircase–Escalante National Monument of southern Utah, and it is divided into several members (Lower, Middle, Upper, Capping Sandstone; Fig. 9.1) (Jinnah and Roberts, 2011). Deposition of this unit took place between ~81–77 Ma, based on a dated volcanic ash bed, detrital zircons, and estimated sedimentation rates (Jinnah et al., 2009). Although it is slower to produce fossil material, this formation is providing important information on the hadrosaurid dinosaurs that lived in southern Utah during the early and middle Campanian (Gates et al., 2013). One of the most significant taxa is a new saurolophine named Acristavus gagslarsoni, which is currently the earliest member of a small clade that contains this taxon and the hadrosaurids Maiasaura peeblesorum and Brachylophosaurus canadensis (Gates et al., 2011). Several other hadrosaurid specimens have been located within the Wahweap in addition to the referred specimen of Acristavus (UMNH VP 16607).

This chapter describes specimens from two of these sites, both briefly mentioned in Gates et al. (2013) but not described in detail or discussed in reference to the taxonomy of Prieto-Márquez (2010a). An isolated lambeosaurine maxilla is described here as the second new hadrosaurid species from the Wahweap Formation. A bonebed that preserves two individuals of a possible new species is also documented. These specimens increase the known hadrosaurid diversity in the southern region of the Western Interior Basin during the middle Campanian. Institutional Abbreviations AMNH, American Museum of Natural History, New York; CPC, Colección Paleontológica de Coahuila (Paleontological Collection of Coahuila) Saltillo, Coahuila, Mexico; MOR, Museum of the Rockies, Bozeman, Montana; NCSM, North Carolina Museum of Natural Sciences, Raleigh, North Carolina; RAM, Raymond M. Alf Museum of Paleontology, Claremont, California; ROM, Royal Ontario Museum, Toronto, Ontario; TCMI, Children’s Museum of Indianapolis, Indianapolis, Indiana; TMP, Royal Tyrrell Museum of Palaeontology, Drumheller, Alberta; 9-Hadrosaurs Ch9 (154-73).indd 156 8/28/14 1:22 PM Copyrighted Material. (c) 2014 Indiana University Press. All Rights Reserved.New Hadrosaurid Specimens from the Wahweap Formation 157 9.1. Composite stratigraphic section of the Wahweap Formation. Hadrosaurid specimens discussed in text are labeled reflecting their stratigraphic occurrences. The locality of UCMP 152028 is unknown, but based on an examination of the host matrix it is likely to have originated from the Upper Member. Death Ridge is a locality that has produced at least one hadrosaurid (not mentioned in the text) and several other important fossils. UCMP, University of California Museum of Paleontology, Berkeley, California; UMNH, Natural History Museum of Utah, Salt Lake City, Utah.

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